1. Field of the Invention
This invention relates to a method and a device for processing video signals and to a recording medium on which is recorded a program for processing the video signals.
2. Description of Related Art
A picture editing device, termed a non-linear video editing device, is already put on the market. This non-linear video editing device, provided with a disc-shaped recording medium, such as a hard disc, as a temporary recording medium used in editing, is randomly accessible, thus enabling non-sequential non-linear editing. In such non-linear video editing device, a desired image material may be read out promptly, whilst the image material can be inserted and removed easily to or from a continuous image material.
However, in the conventional non-linear video editing device, there are imposed limitations such that a user is compelled to use a sole format of image data, or such that, even though the user is allowed to use plural formats, image data has to be transformed to common format data in case of performing image processing of specified effects or total effects, such as, for example, transition effect.
In the former case, if the user is compelled to use a sole format, the user is unable to select the format freely, thus imposing a load on the user.
In the latter case, the processing of transforming the format to a common format is in need of significant overhead in processing or deteriorates the video image quality.
Especially, an image format, which is based on the discrete cosine transform (DCT), such as so-called MPEG (Moving Picture Experts Group), so-called JPEG (Joint Photographic Coding Experts Group), so-called H.261 or the so-called DV (Digital Video), uses quantization of DCT coefficients in a portion of the compression processing.
In an ordinary technique of the general-purpose editor, th image format is restored into pixel (picture element) representation and picture processing is executed in a spatial area to compress the picture again by way of re-encoding. However, re-quantization of DCT coefficients in encoding and rounding to integers lead to image distortion, which keeps on to be accumulated from generation to generation.